Questions and postings pertaining to the usage of ImageMagick regardless of the interface. This includes the command-line utilities, as well as the C and C++ APIs. Usage questions are like "How do I use ImageMagick to create drop shadows?".
Apologies. quantumOperator() will subtract a constant value from an image. To subtract one image from another, use compositeImage() with the SubtractCompositeOp operator.